VFS: note error returns in documentation for various lookup functions

Darrick recently noted that try_lookup_noperm() is documented as
"Look up a dentry by name in the dcache, returning NULL if it does not
currently exist." but it can in fact return an error.

So update the documentation for that and related functions.

Link: https://lore.kernel.org/all/20260218234917.GA6490@frogsfrogsfrogs/
Cc: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: NeilBrown <neil@brown.name>
Link: https://patch.msgid.link/20260224222542.3458677-2-neilb@ownmail.net
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/namei.c b/fs/namei.c
index 58f715f7657e27d67a15705af09d5d1a91507daa..6f595f58acfea542440ba6589df7e9979854c36c 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3124,7 +3124,8 @@ static int lookup_one_common(struct mnt_idmap *idmap,
  * @base:      base directory to lookup from
  *
  * Look up a dentry by name in the dcache, returning NULL if it does not
- * currently exist.  The function does not try to create a dentry and if one
+ * currently exist or an error if there is a problem with the name.
+ * The function does not try to create a dentry and if one
  * is found it doesn't try to revalidate it.
  *
  * Note that this routine is purely a helper for filesystem usage and should
@@ -3132,6 +3133,11 @@ static int lookup_one_common(struct mnt_idmap *idmap,
  *
  * No locks need be held - only a counted reference to @base is needed.
  *
+ * Returns:
+ *   - ref-counted dentry on success, or
+ *   - %NULL if name could not be found, or
+ *   - ERR_PTR(-EACCES) if name is dot or dotdot or contains a slash or nul, or
+ *   - ERR_PTR() if fs provide ->d_hash, and this returned an error.
  */
 struct dentry *try_lookup_noperm(struct qstr *name, struct dentry *base)
 {
@@ -3208,6 +3214,11 @@ EXPORT_SYMBOL(lookup_one);
  *
  * Unlike lookup_one, it should be called without the parent
  * i_rwsem held, and will take the i_rwsem itself if necessary.
+ *
+ * Returns: - A dentry, possibly negative, or
+ *         - same errors as try_lookup_noperm() or
+ *         - ERR_PTR(-ENOENT) if parent has been removed, or
+ *         - ERR_PTR(-EACCES) if parent directory is not searchable.
  */
 struct dentry *lookup_one_unlocked(struct mnt_idmap *idmap, struct qstr *name,
                                   struct dentry *base)
@@ -3244,6 +3255,10 @@ EXPORT_SYMBOL(lookup_one_unlocked);
  * It should be called without the parent i_rwsem held, and will take
  * the i_rwsem itself if necessary.  If a fatal signal is pending or
  * delivered, it will return %-EINTR if the lock is needed.
+ *
+ * Returns: A dentry, possibly negative, or
+ *        - same errors as lookup_one_unlocked() or
+ *        - ERR_PTR(-EINTR) if a fatal signal is pending.
  */
 struct dentry *lookup_one_positive_killable(struct mnt_idmap *idmap,
                                            struct qstr *name,
@@ -3283,6 +3298,10 @@ EXPORT_SYMBOL(lookup_one_positive_killable);
  * This can be used for in-kernel filesystem clients such as file servers.
  *
  * The helper should be called without i_rwsem held.
+ *
+ * Returns: A positive dentry, or
+ *        - ERR_PTR(-ENOENT) if the name could not be found, or
+ *        - same errors as lookup_one_unlocked().
  */
 struct dentry *lookup_one_positive_unlocked(struct mnt_idmap *idmap,
                                            struct qstr *name,
@@ -3311,6 +3330,10 @@ EXPORT_SYMBOL(lookup_one_positive_unlocked);
  *
  * Unlike try_lookup_noperm() it *does* revalidate the dentry if it already
  * existed.
+ *
+ * Returns: A dentry, possibly negative, or
+ *        - ERR_PTR(-ENOENT) if parent has been removed, or
+ *        - same errors as try_lookup_noperm()
  */
 struct dentry *lookup_noperm_unlocked(struct qstr *name, struct dentry *base)
 {
@@ -3335,6 +3358,10 @@ EXPORT_SYMBOL(lookup_noperm_unlocked);
  * _can_ become positive at any time, so callers of lookup_noperm_unlocked()
  * need to be very careful; pinned positives have ->d_inode stable, so
  * this one avoids such problems.
+ *
+ * Returns: A positive dentry, or
+ *        - ERR_PTR(-ENOENT) if name cannot be found or parent has been removed, or
+ *        - same errors as try_lookup_noperm()
  */
 struct dentry *lookup_noperm_positive_unlocked(struct qstr *name,
                                               struct dentry *base)